題目鏈接：http://hihocoder.com/problemset/problem/1616

題解：就是簡單的模擬一下至於如何判斷是不是二叉搜索樹可以通過中序遍歷將每個點存下來看是不是遞增的如果是遞增的就是反之不是

#include <iostream>
#include <cstring>
#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
const int M = 1e4 + 10;
vector<int
 
> vc[M];
int fa[M] , ch[M][2] , f[M] , n , emmm , num[M];
void init() {
    for(int i = 1 ; i <= n ; i++) {
        f[i] = i;
        vc[i].clear();
    }
}
int find(int x) {
    if(x == f[x]) return f[x];
    return f[x] = find(f[x]);
}
int cnt;
void cau(int u) {
    int len = vc[u].size();
    
 
if(len == 2) {
        if(vc[u][0] == vc[u][1] || vc[u][0] == u || vc[u][1] == u) emmm = 1;
        cau(vc[u][0]);
        num[cnt++] = u;
        cau(vc[u][1]);
    }
    if(len == 1) {
        if(vc[u][0] == u) emmm = 1;
        if(vc[u][0] > u) {
            num[cnt++] = u;
            cau(vc[u][
 
0]);
        }
        else {
            cau(vc[u][0]);
            num[cnt++] = u;
        }
    }
    if(len == 0) {
        num[cnt++] = u;
    }
}
void dfs(int u) {
    int len = vc[u].size();
    if(len == 1) {
        if(u > vc[u][0]) {
            putchar(‘(‘);
            printf("%d" , vc[u][0]);
            dfs(vc[u][0]);
            putchar(‘)‘);
            putchar(‘(‘);
            putchar(‘)‘);
        }
        else {
            putchar(‘(‘);
            putchar(‘)‘);
            putchar(‘(‘);
            printf("%d" , vc[u][0]);
            dfs(vc[u][0]);
            putchar(‘)‘);
        }
    }
    if(len == 2) {
        putchar(‘(‘);
        printf("%d" , vc[u][0]);
        dfs(vc[u][0]);
        putchar(‘)‘);
        putchar(‘(‘);
        printf("%d" , vc[u][1]);
        dfs(vc[u][1]);
        putchar(‘)‘);
    }
    if(len == 0) {
        putchar(‘(‘);
        putchar(‘)‘);
        putchar(‘(‘);
        putchar(‘)‘);
    }
}
int main() {
    int t;
    scanf("%d" , &t);
    while(t--) {
        cnt = 0;
        scanf("%d" , &n);
        memset(fa , -1 , sizeof(fa));
        int flag = 0;
        init();
        for(int i = 1 ; i <= n - 1 ; i++) {
            int u , v;
            scanf("%d%d" , &u , &v);
            vc[u].push_back(v);
            int a = find(u) , b = find(v);
            if(a == b) {
                flag = 1;
            }
            else {
                f[b] = a;
            }
            if(fa[v] == -1) {
                fa[v] = u;
                continue;
            }
            else {
                flag = 1;
            }
        }
        if(flag) {
            printf("ERROR1\n");
        }
        else {
            int tmp = 0;
            for(int i = 1 ; i <= n ; i++) {
                if(vc[i].size() == 0) continue;
                sort(vc[i].begin() , vc[i].end());
                if(vc[i].size() > 2) {
                    tmp = 1;
                    break;
                }
            }
            if(tmp) {
                printf("ERROR2\n");
            }
            else {
                emmm = 0;
                int root = 1;
                for(int i = 1 ; i <= n ; i++) {
                    if(fa[i] == -1) {
                        root = i;
                        break;
                    }
                }
                cau(root);
                for(int i = 1 ; i < cnt ; i++) {
                    if(num[i] <= num[i - 1]) {
                        emmm = 1;
                        break;
                    }
                }
                if(emmm) {
                    printf("ERROR3\n");
                }
                else {
                    putchar(‘(‘);
                    printf("%d" , root);
                    dfs(root);
                    putchar(‘)‘);
                    puts("");
                }
            }
            
        }
    }
    return 0;
}

hihocoder 是二叉搜索樹嗎？(模擬題)